Oscillator and frequency modulator



June 18, 1946. M. G. CROSBY 2,402,148

OSCILLATOR AND FREQUENCY MODULATOR Filed Nov. 24, v1943 2 Sheets-Sheet 1 BY m ATTORNEY June 18, 1946. M. G. CROSBY 2,402,148

QSCILLATOR AND FREQUENCY MODULATOR Filed Nov. 24, 1945 2 Sheets-Sheet 2 \NVENTOR Mae/e4) G- [Pwa Y.

BY )i mw ATTORNEY Patented June 18, 1946 oscmts'roa sun successor monuns'roa- Murray G. Crosby, Itiverliead, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application November-24, 194s. Serial No. more 13 Claims. (01. 179-1715) A general. object of the invention is to improve oscillation generators. More specifically, an obiect of this invention is to provide a stabilized oscillation generator such as a crystal controlled generator which is tunable over a small frequency range.

This object is attained by connecting a pair of tubes in a circuit including a crystal, such that each tube operates alone and the two tubes or crate at different frequencies but are so coupled and entrained that the circuit'assumes a mean frequency of operation as in Hansell U. S. Patent #1381979, dated'October "I, 1930. The relative element voltages of the.two tubes are differentially varied to thereby vary the frequency at which the two oscillators are entrained.

together and connected in parallel to a tuned circuit Ill from which the output may be taken. The screening electrodes G and G are connected to points on two potentiometers '40 and '42 con- A second object of the present invention is to I provide with the oscillator described above a timing modulation system.

This object is attained by using. as the voltage applied differentially to the tube electrodes, modulating potentials. Other objects and the manner in which the same are attained along with advantages gained by the use thereof will appear from the detailed description which follows.

in this description reference will be made to nected'for simultaneous adjustment. 1 The, poten-' tiometers 40 and 42 are connected with a source of supply so that variation of the points thereon varies in a differentialmannerthe potentials on the. screening. electrodes of tubes ill and I2. The potentiometer, that is, the bias source for the screening electrodes is shunted by RF bypassing condensers BP. v

Fig. 2 shows the impedance versus frequency characteristic of the crystal at point A, and of the circuit L, Cl, C2 at point B. Thecurve, shown dotted, is the inverse impedance characteristic of the'crystal due to the impedance inverting characteristics of network L, Cl, C2. This network has the property of exhibiting a high impedance at its outputi B when a low impedance appears at its input A. The impedance-charac-- teristic of the crystal taken alone is shown by the solid curve in P18. 2. The inverted characteristic appearing at the point B of the network the attached drawings, wherein Fig. 1 illustrates by circuit diagram an oscillator arranged in accordance with my invention. The oscillator in eludes means for adjusting the frequency of operation.

Fig. la illustrates a modification of a portionof the circuit of Fig. 1. In Fig. 1a is shown means for controlling the frequency of operation of the oscillator in accordance with the signals when the generated oscillations are to be modulated as to frequency.

Fig. 2 is a graphillustrating the operation of the frequency determining circuits in the oscillators of Figs. 1 and 3.

Fig. a is a modified oscillation generator utilizifin lg tihe principle involved in the generator of In Fig. 1, II and i2 are two electron discharge devices having their control grids coupled to the terminals of a reactive circuit including inductis shown by the dotted curve. The result of this connection of the crystal and impedance-inverting network is this pair of impedance characteristics in which the high impedance point of one (the crystal) is at frequency F2. The high impedance point of the other (the output of the network at B) is at frequency Fl. These two impedance characteristics appear at the grids of tubes l0 and I2 to oscillate in conjunction with the common plate circuit It in a generator circuit using capacity feedback. I

. For instance, if tube It were switched off and tube l2 allowed to oscillate, the circuit would oscillate at the high impedance point of the crystal or at frequency F2. .If tube i2 were switched off and tube it allowed to oscillate; 0s-

.cillations would take placeat the high impedtiomet'erarrangement the amplification of one tube may be reduced andthat of the other increased so as to swing the frequency of oscillation towards the frequency of maximum impedance 'cillotion takes place otthc in:

'quency of oscillation may be varied het secures the electrode capacity of the crystol holder. ll

this electrode capacity were removed only the resonant frequency Ft would appear. For low values of electrode cenecity Fl and F2 ore far apart, and for higher values the spacing becomes closer. The velueof this electrode conocity my be controlled by making it a. port of tuned cir= cult Li, 6333. I

Thus, if Ll, C8 are tuned so that CZ; together with the electrode cepecity forms o. tuned circuit which tunes to the resonont ireouency oi the crystal, the effect of the electrode cepecity will be removed. If this tuning is sluited to one side of the resonant frequency of the crystol o concc= itive or inductive efiect appears ccross the crystal to form on snti-resonent peel: shove or helow the resonant frequency or the crystal. The ire quencydifierence between the resonant dip and the anti-resonant peel: may be controlled by the amount or. detuniug of tuned circuit Ll, C8. Thus the frequency range between li l and F2 may be controlled b a variation of C8.

When it is desired to produce frequency modu lotion with the circuit of Fig. l transformer 50 of Fig. lc may be substituted for the pctentiom eter arrangement flit-42 in. Fig. i. This suhsti= tution is made by breaking the leads to notch. tiorneter at end 62 ot the points worked by crosses and connecting the secondary winding or 66 to these points in piece of the resistrmces and G2.

Modulation potentials are fed to lock 69 through the transformer to the screen grids of the oscillator tunes to eficct s. difrerentiol modu lotion of the screen grids. This diderentiol moduletion reduces the amplification oi one tube while it increases that of the other. The result is 9. frequency modulation over the range hettreen Fl. and F2 in Fig. 2.

In case it is desired to concrete oscllletions the frequency ofwhich may be i: -ged throuch it limited range the simplified orrongernent ot Flo.

' c stunts or thickness oi the crystal itself. The outout is token ct leods so.

As described in connection with Fig. l, tuned circuit Ll, C53 is tuned to nearly tuneout the electrode copcclty of the crystal oscillator, and the tuning reectonce C3 may be varied to change the succinct between Fl and F2 and thereby vary the reuse over which the frequency of the genorator moy be varied.

I claim:

- i. In on oscillation generator, an impedance inverting network comprising series reectence and shunt reoctence, o piezo electric crystal across one terelof the network, the sold crystal clone hot/int. c civen'impedonce against frequency characteristic, the crystol and impedance invertinc networl: providing at the other end of sold network at corresnonding chorocteristicinverted, on output circuit, an electron discherge system in on oscillation generator including sold network as o frequency controlling means and con motions for utilizing in sold generotor either of the sold impedance characteristics thereoi.

2. in on oscillation generator and frequency niodulotor, on impedance inverting network com prising series reoctence and shunt reacts-once, a piece electric crystal across one terminal oi the network, the sold crystal clone having a. given iinnedence eooinst frequency characteristic, the crystcl and impedance inverting network providingct the other end of sold network a. correspending characteristic inverted, an output cir= cult, on electron discharge system in on oscillotion generator including said network a e in.-

ouency controfliru; moons, connections for utilizing in solo. generator either or the sold impsd= once versus frequency characteristics thereof and connections from a. source of modulating pote tiols to on electrode in sold discharge system to modulote gain thereo to thereby modulate the ireuueucyof the oscillations generated.

13. In an oscillation generator, an impedance inverting network comprising series inductance 3 may be used. In this orrengement c single tulce 64 is arranged to oscillate with o grid circuit in which a. sliding contact to on the impedance inverting-network-inductence L varies the impedence between the high impedance point or the crystal characteristic at A or its invertedim pedence at B in the output or the network With the slider it on point A, that is ot the crystol end of the impedance inverting network, the no once characteristic at the grid so or the oscillator tube 5 3 is thetoi the solid line in Fig. 2. With the slider on point B that is at the of the impedance inverting networi; etc from .the crystal, the chorocterlstlc at the d to is as shown by the dotted line curve or Fla. 2.

ial of mum frequency which would he frcouency rd when the slider is on point A illlfli'l at Ft when the slider is on point B. When the slider is at intermediate points oscillation tclres place in the range between Fl and W. In. this way the ire= an" 33 mo quency Fl and. F2 without calm: the conend shunt conecity, e, piezo electric crystal in o holder across one terminal of the networl-z, the

said crystol alone having u given impedance eeeinst frequency characteristic, the sold crystal and impedance inverting network providing at the other end of the network a. corresponding chorocteristic inverted, on. output circuit, an elec-, tron dischorce system in on oscillation generator including sold network as o frequency controlling moons and e vorioble reoctence in shunt to said crystol holder to tune the capacity thereof.

o. In an oscillation generator and frequency niodulotor, on impedance inverting network comprising series inductance and shunt capacity, .9. piezoelectric crystal in c. holder across one terminal oi the network, the sold crystal clone having or given impedance against frequency chorocterletic, the sold crystal and impedance inverting network providing at the other end of the network at corresponding characteristic ln= verted, on output circuit, an electron discharge system in on oscillation generator including said network as a frequency controlling means, o vorioble rccctcnce in shunt to sold crystol holder to tune the capacity thereof and at source of modulating potentials coupled to said dlschorge inverting." network comprising series inductance end shunt capacity, a piece electric crystal across and output electrodes including an anode, a

one terminal of the network, the saidcrystal alone having a given impedance against frequency characteristic,'the said crystal and impedance inverting network having a corresponding characteristic inverted, an output circuit, an electron discharge system in an oscillationgenerator including said network as a frequency controlling means and connections for utilizing as said frequency controlling means either of the impedance versus frequency characteristics thereof or the mean thereof.

6. In an oscillation generator, two electron discharge systems each having input electrodes including a control grid and output electrodes including an anode, a tuned circuit, connections tying said anodes together and to'said tuned circuit, an impedance inverting network coupled between the control grids of said systems, a reactance at one, end of said network having a given impedance versus frequency characteristic, and connections for varying the gains of said systems differentially.

7. In an oscillation generator, two electron discharge systems each having input electrodes including a control grid and'output electrodes including an anode, a tuned circuit, connections tying said anodes together and to said tuned circuit, an impedance inverting network coupling between the control grids of said systems, a piezo electric crystal shunting one end of said network, and connections for varying the gains of @said systems differentially.

8. In an oscillation generator, two electrondischarge systems each having input electrodes including a control grid and output electrodes including an anode, a tuned circuit, connections tying said anodes together and to said tuned circuit, an impedance inverting network coupling between the control grids of said system, a piezo electric crystal in a holder in shunt to one end of said network, a tuning reactanoe in shunt to the crystal holder, and connections for varying the gains of said systems differentially.

9. In an oscillation generator and frequency modulator, two electron discharge systems each having input electrodes including a control grid circuit, connections tying said anodes together and. to said tuned circuit, an impedance inverting network coupling betwe'en the control grids of said tubes. at piezo electric crystal in a holder in shunt to one end of said network, a tuning reactanoe in shunt to the crystal holder, a source of modulating potentials, and connections between corresponding electrodes in said systems and said source'of modulating potentials for differentially modulating the potentials on said corresponding electrodes.

minal thereof, connections coupling the control grid of one of said systems to one terminal of said network and the control grid of the other of said systems to the other terminal of said network and connections for modulating the gains of said discharge systems differentially in accordance with signals.

11. In a timing modulation system, an oscil lation generator including two electron discharge tubes each having input electrodes including a control grid and having output electrodes including an anode and having an additional electrode, an output circuit connecting the output electrodes in parallel, an impedance inverting network, a piezo electric crystal across one terminal thereof, connections coupling the control grid of one of said tubes to one terminal of said network and the control grid of the other of said tubes to the other terminal of said network, and connection between the additional electrodes oi said tubes and a source of modulating potentials for diil'erentially modulating the gains of said tubes.

12. In an oscillation generator, an impedance inverting network, apiezo' electric crystal in a holder across one terminal of the network, the

said crystal alone having a given impedance against frequency characteristic, the said crystal and impedance inverting network providing at the other end of the network a substantially cortuned I responding characteristic inverted, an output circuit, andan electron discharge system in an oscillation generator including said network as a frequency controlling means.

13. In an oscillation generating system, an im- 'pedance inverting network having at its one end a crystal which has a given impedance versus frequency characteristic, said network having at its other end said impedance versus frequency characteristic inverted,'said crystal being in a holder exhibiting capacity which is in said network, a variable reactanoe in said network for tuning the capacity of the crystal holder so that the same is, tuned out or exhibits acrossthe crystal an efiect which is capacitive or inductive depending ,upon the said tuning, an electron discharge system having electrodes coupled by said crystal and network for the production of oscillations, and'an output circuit coupled to electrodes of said discharge system.

MURRAY G. CROSBY. 

